1. Field of the Invention
The present invention relates to a thin film transistor. More particularly, the present invention relates to a thin film transistor having high carrier mobility and favorable reliability.
2. Description of Related Art
With rapid progress in semiconductor manufacturing techniques, various displays have been continuously launched. To satisfy requirements of lightness, slimness, shortness, compactness, portability, and so on, the displays characterized by flexibility and convenience in carrying have become the dominant type in the next generation of the displays. For instance, development of flexible displays and electronic papers are have gradually concerned by manufacturers. Specifically, thin film transistors are widely used in displays and performance of the thin film transistors is affected by the structural designs or the material of the thin film transistors directly.
Generally, the thin film transistor at least include a gate, a source, a drain, and a channel layer, wherein conductivity of the channel layer is determined by the voltage applied to the gate. Specifically, the source and the drain are electrically conducted with each other when the channel layer is turned on or electrically insulated from each other when the channel layer is turned off. In addition, an N-doped ohmic contact layer or a P-doped ohmic contact layer may be usually formed on the channel layer so as to reduce contact resistance between the channel layer and the source/drain. In conventional thin film transistors. the material of the channel layer of the thin film transistors includes amorphous silicon (α-Si) or poly-silicon (p-Si).
Regardless the channel layer is made from amorphous silicon (α-Si) or poly-silicon (p-Si), high process temperature is required when thin film transistors are fabricated. For instance, the process temperature is greater than 280 degrees centigrade when the channel layers of the thin film transistors are made from amorphous silicon (so-called α-Si TFTs). Accordingly, when α-Si TFTs are used in the application of flexible displays, flexible substrates (e.g. plastic substrate) of flexible displays are deteriorated or deformed resulted from high process temperature. In other words, conventional α-Si TFTs are not suitable for application of flexible displays. On the other hand, application of conventional α-Si TFTs are restricted due to poor carrier mobility (less than 1 cm2/V-s) and reliability thereof.